What is Gold Plating?
Gold is a rare high value material which is the most malleable of all the metals.
Gold plating originated from the Egyptians, but this was in the form of a hammered film on other metals. In the Middle Ages sword handles or artefacts were coated with a mercury/gold amalgam. The parts were heated to drive off the mercury and leave a layer of pure gold. The gold film was burnished to obtain a bright finish. This method was dangerous and many people lost their lives due to the toxicity of the mercury. The first true electroplating was achieved in the middle of the nineteenth century.
Gold Plating Finish Benefits
- It has a high corrosion resistance.
- It does not form an oxide film on its surface and has a low contact resistance.
- The finish can be either bright or dull.
- In the electronics industry it is used for protection from corrosion to provide a conductive layer on copper or brass.
- To prevent tarnishing, nickel is deposited first and provide a base for the gold and improve wear resistance.
Types of Gold Plating
The purity of gold is measured in karat numbers eg 18 or 24 karat, 24 karat is pure gold.
18 karat is 75% gold and other metals such as silver, copper, zinc, platinum or palladium.
There are various types of gold plating solutions that produce different finishes.
Alkaline gold solution containing cyanide producing a gold and gold alloy plate.
Neutral solution also containing cyanide for high purity soft gold plate. The hardness is about 60-85.
Acid solutions produce a hard gold plate with a hardness of about 120-130. The bath can comprise a small amount of nickel and/or cobalt too.
The non-cyanide solutions are normally sulphite or chlorine based.
For decorative purposes a thickness of 0.1-0.2 microns is deposited. Heavier deposits can be obtained but the thicker the plate the more expensive it becomes.
Gold Plating Finish Main Uses
The main applications are:
- watch cases,
- bathroom fittings
- scientific appliances
- electronics etc.
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